<!DOCTYPE html>
<html>
<head>
<!-- External css file needed to trigger a css cache image load -->
<link href="fetch-insecure-css-image.css" rel="stylesheet" type="text/css" />
</head>
<body>
<img id="insecure-css-img">
<script>
window.addEventListener("load", function() {
    if (parent.window)
        parent.window.postMessage('done', '*');
}, false);
</script>
</body>
</html>